The present invention relates generally to fluid valves and, more specifically, to an electro-thermally operative gaseous fuel valve with a mechanism for closing the valve when excessive energizing power is supplied thereto.
One type of thermal fuel valve is disclosed in U.S. Pat. No. 3,870,457. As disclosed in that patent, the thermal fuel valve, for example, may be used with an electric igniter device in a gas range appliance or the like to control gas flow while the igniter provides automatic gas ignition at a burner without the need for a continuously burning, fuel wasting pilot light, thereby saving substantial amounts of fuel when the appliance is not in use. The electric igniter, which is positioned proximate a burner of such an appliance, and an internal electric heater in the thermal fuel valve enclosure, which is positioned to heat a thermally responsive heat warpable member or actuator that moves the poppet to open the valve, are desirably connected for series electric energization. Therefore, the thermal fuel valve will open and allow gas to flow to the burner only when the electric igniter has been energized and preferably the valve is calibrated or adjusted to open only when the igniter is near or at a temperature suitable for igniting the gaseous fuel. Moreover, since the force required to be exerted by the actuator to move the poppet from its seat is usually dependent on the gas pressure in the valve, such calibration normally would take into consideration the normal gas pressure.
Since an appliance incorporating such a valve arrangement as disclosed in that patent does not experience any fuel flow in the fuel circuit between the appliance fuel input connection and the burner unless the valve is open, the pressure regulator in that fuel circuit, which is usually located between the fuel input connection and the thermal fuel valve, may not operate properly to regulate the fuel pressure until the valve opens to allow fuel flow. While satisfactory fuel flow to the pilot light in prior art ranges will maintain the pressure regulator operable, or nearly so, complete closure of fuel flow in ranges or the like in which no pilot lights are used may cause a relatively high pressure at the fuel valve under a no flow condition, which may impede valve opening.
Accordingly, a snap-acting type thermal fuel valve, which is effectively operable over a relatively wide range of gas pressures, for example, on the order of from about four inches to about twenty inches on a water column, to assure valve opening and closing without concern for pressure variation in that range, is disclosed in U.S. patent application Ser. No. 653,477 for "Thermal Valve," filed Jan. 29, 1976, assigned to the same assignee as the present application. The thermal fuel valve disclosed in that Application employs an over-center mechanical energy storage and release mechanism to effect snap opening and snap closing of the valve poppet. When heated, the heat warpable member of such valve compresses a constrained spring while relatively moving its pivot points so as to effect an over-center traveling thereof whereupon some of the energy stored in the spring is relatively rapidly released to snap open the poppet. Calibration of such a snap-acting thermal fuel valve coordinates valve opening, ass determined by the relative spacing of the spring pivot points and the amount of relative movement thereof to pass the center position, with the igniter temperature without substantial concern for the gas pressure in the valve enclosure.